In the use of gas generators or rocket motors of the solid propellant type, there often arises a need for varying the time vs. output or thrust of the device. This has usually been attempted by reduction or enlargement of the area of the exit by using movable pieces as are shown in U.S. Pat. No. 3,760,589 to Puckett et al where a sliding piston is adapted to be moved in and out of ports leading from the combustion chamber to the exit nozzle, or, by deflecting hinged restrictors into the exhaust stream at the exit nozzle as in U.S. Pat. No. 2,894,692 to Ledbetter et al. Bulb type nozzle restrictors are also used in the art as exemplified in the U.S. Pat. No. 2,637,973 to Lawrence. Each of these, however, have common problems associated with them such as inaccuracy of the exact time vs. output relationship desired, binding or sticking of the parts due to heat expansion or warping, general complexity of structure, excessive weight and large space envelopes.
The present invention on the other hand provides a simple but effective device for changing the time-output relationship to accord with a predetermined time vs. output or thrust profile by the rotation of a rotary valve from one position to another to direct the flow of gases from the combustion chamber into and through individually pre-calibrated discrete primary nozzles and thence into and through the exit, usually a nozzle or nozzles. Since each primary nozzle has its particular characteristics and each is selected and used individually, the selection of any particular one accurately reproduces that particular time-output relationship or profile by establishing the combustion chamber pressure of the overall gas generator or motor. The resulting gas generator or motor thus very accurately achieves its desired results in a structure which minimizes weight, complexity and required space envelope and should improve reliability because of its single major moving part.
Exact time vs. thrust profile rocket motors are particularly useful as motors for decoy missiles where the discrete profiles are essential to provide information which will be misleading and thus tend to obscure the profile characteristics of the main or actual missile or at least to make it more difficult to identify it.